Method of cooling pellets

ABSTRACT

A pellet cooling system including a novel coolant cage construction and operational manner so as to insure the cooling of warm thermoplastic pellets as they emerge from a die head and are cut by rotating knives is disclosed. After cooling, as by entrainment in coolant flows simultaneously directed peripherally about the cage sides and radially across the front face thereof, the pellets are immediately withdrawn from the cage. Additionally, a feature of the coolant cage is the provision of a novel slinger for distributing a coolant flow evenly over its front face.

This is a division of application Ser. No. 748,235 filed Dec. 6, 1976,now U.S. Pat. No. 4,099,900.

BACKGROUND OF THE INVENTION

This invention relates to a construction and manner of formingthermoplastic pellets, including means for extruding strands ofthermoplastic material substantially into an air or other gaseousenvironment enclosing chamber as contrasted to a liquid coolantsubmerged system. The strands are cut or broken into discrete particlesor pellets by rotating knives, subsequently entrained in coolant flowsand thereafter removed from further processing. The invention isparticularly directed to a novel pellet cage construction for coolingand collecting such thermoplastic pellets and the manner in which suchcooling is performed so as to reduce and/or prevent collision of suchpellets prior to or during their cooling. Such action prevents thepellets from sticking together when hot to form multiple clustersthereof. Clusters are undesirable in later processing, such asconveying, weighing and feeding to subsequent extrusion operations.

A number of pellet cage designs are available, generally for the samepurposes as above indicated, including that disclosed in U.S. Pat. No.3,343,213 issued Sept. 26, 1967, which discloses the use of a coolinghood of substantially circular cross section in which pellets emergingfrom an adjacent extrusion die head are entrained in a single spiralingcoolant flow. The pellets are progressively moved from their point ofcontact with the side walls of the hood forwardly therealong in suchspiral motion to an exit at the forward end of the cage. The presentapplicants have found, however, that by eliminating the forwardspiraling progression of such entrained pellets that the dwell time inwhich the pellets are present within the cage and the length of the cageitself can be substantially reduced and that highly effective cooling toprevent the above-referred-to cluster problem can be produced by thesimultaneous provision of multiple coolant flows, one in a peripheralpattern about the inner walls of the cage, and the other in a radiallyoutward pattern to cover the adjacent front face thereof. Newly formedpellets projected against either of such wall surfaces are accordinglyimmediately entrained in a coolant flow and are thereafter immediatelyupon completion of their arcuate travel about the periphery of the innerwall surfaces removed from the cage so as to not interfere with theeffective cooling and removal of subsequent pellets.

It is accordingly an object of the present invention to provide acoolant cage of novel construction which enables thermoplastic pelletsformed by extrusion and cutting means in operative association therewithto be cooled and removed therefrom in a minimum dwell time, yet assuringeffective cooling so as to prevent formation of pellet clusters.

A further object of the present invention is the provision of a coolantcage for the receipt, cooling and minimum retention of thermoplasticpellets projected thereinto by an adjacent operatively associatedthermoplastic strand extrusion and cutting means, wherein the pellets soprojected initially contact either interconnected peripheral side orforward internal surfaces of such cage which cooperatively form achamber for receipt of such pellets, which surfaces are bothsimultaneously provided with flows of liquid coolant thereover.

Still another object of the present invention is the provision of acoolant cage construction of the immediately aforementioned type,wherein means are provided for projecting a first coolant flow in asubstantially single-path peripheral orbit about and in contact with amajor portion of said internal side surfaces, whereby pellets entrainedtherein are immediately removed from such coolant cage without thenecessity of forwardly advancing them along such side walls in a spiralattitude.

Another object of the present invention is the provision of a method ofcooling thermoplastic pellets by their receipt and entrainment in one ofa plurality of simultaneously provided fluid coolant flows providedabout the side and front face internal surfaces of a coolant cage, andthereafter immediately withdrawing such entrained pellets so as toreduce the dwell time therein.

A still further object of the present invention is the provision of anovel slinger device which enables the front face of a coolant cageconstruction adapted for receipt of thermoplastic pellets emerging froman operatively associated thermoplastic extrusion and cutting means tobe provided with an even flow of liquid coolant in an efficient mannerwith minimal power requirements.

SUMMARY OF THE INVENTION

The above objects are substantially met by the provision of a pelletcage for cooling and collecting thermoplastic pellets formed by thecutting of strands of thermoplastic material emerging from the die faceof an extruder or the like by means of rotating cutters or the likewhich project said pellets in a generally radially outward downstreamtrajectory, said cage comprising a hood having interconnected peripheralside and forward internal surfaces and positioned with respect to saiddie face so as to form an enclosed chamber immediately downstreamthereof for confining the receipt of said pellets as they are formed,first means for projecting a flow of coolant in a substantially singlepass, peripheral orbit about and in contact with a major portion of saidinternal side surface, and second means for simultaneously projecting asecond flow of coolant over and in contact with a major portion of saidinternal forward surface so as to contact substantially all of saidemerging pellets with one or both of said coolant flows to cool them,and means for continuously withdrawing said cooled pellets from saidchamber. Additionally, the manner of withdrawing said pelletscontinuously and generally in less than a single orbit about saidperipheral side surfaces contributes to the minimum dwell time in whichsuch effective cooling is accomplished. Furthermore, the provision of arotating hub or flange construction having a plurality of spaced baffleswhich are adapted to receive one or more coolant flows directedgenerally tangentially contributes to the even and complete distributionof coolant about the front face of the pellet cage in a manner effectivein achieving desirable cooling action with minimum power requirements.

Other objects, features and advantages of the invention shall becomeapparent as the description thereof proceeds when considered inconnection with the accompanying illustrative drawings.

DESCRIPTION OF THE DRAWINGS

In the drawings which illustrate the best mode presently contemplatedfor carrying out the invention:

FIG. 1 is a side sectional view of a coolant cage constructed inaccordance with the principles of the present invention shown inoperative association with an extrusion and cutting means for theformation of the thermoplastic pellets;

FIG. 2 is a front view with portions broken away from additiveillustration of the coolant cage depicted in FIG. 1;

FIG. 3 is an internal perspective view of a portion of such coolant cageconstruction;

FIG. 4 is a partial perspective view depicting in particular therotating hub associated with the front die face of the extruderassociated with the present invention and further particularly showingthe manner in which the front face of the coolant cage receives evenlydistributed coolant flow thereover by means of the rotating flangehaving a plurality of spaced baffles thereon; and

FIG. 5 is a partial perspective view, on an enlarged scale, withportions broken away, showing in particular the manner in which thecoolant fluid is introduced to the front face of the coolant cage.

DESCRIPTION OF THE INVENTION

Referring to the drawings and in particular FIG. 1 thereof, theconstruction of the extruder and cutting means with which the coolantcage 10 of the present invention is adapted for cooperation is bestshown as including a die 12 having a plurality of extrusion orifaces 14circumferentially spaced about the face 16 of such a die and throughwhich strands of thermoplastic resin material are adapted to beextruded. Thereafter, such strands are chopped, broken or similarly cutinto discrete pellets by the action of rotating knives 18 passing acrossthe face 16 of such die 12 at those points from which the strand emergesfrom the extrusion orifices 14. The knives 18 may be fixed in positionrelative to a generally circular flange 20 of a knife carrier 22 bymeans of bolts 23. The knife carrier 22 is further adapted for rotationwith respect to a fixed hub 24 outwardly extending from central portionsof the die face and affixed thereto as by plate 26 and bolt means 28.Bearings 30 positioned between such stationary hub 24 and the rotatingknife carrier 22 support such rotation and are maintained in suchposition by means of bearing retainers 32 which in turn are supported bythe knife carrier 22 and lock nuts 34 engaged as by threading to the hub24. An adjusting means 36 for the longitudinal positioning of the knives18 with respect to the die face 12 is included and comprise a hubextension 38, an adjustment wheel 40 and retaining means 42. It shouldthus be apparent that the adjusting means 36 is operative tolongitudinally move the knife carrier 22 with respect to the stationaryhub 24 in such a manner so that the positioning of the knives 18 withrespect to the exit portion of the die orifices 14 may be regulated. Theforward end of the knife carrier 22 is further provided with a drivepulley 44 connected thereto as through a drive pulley plate 46, and overwhich a dive belt 48 is trained so as to provide the rotational force atvarious speeds by which the knife carrier 22 may be rotated with respectto the hub 24 and the die 12.

The above apparatus may be that or similar to that disclosed in U.S.Pat. No. 3,981,959 and commonly assigned to the assignee of the presentinvention and may further include the formation of the presentthermoplastic pellets by the novel "Die Quench"™ cooling systemdisclosed in such patent. It should be clear that as the strands ofthermplastic i.e. resin polymer emerge from the die orifices 14 that therotational action of the cutter knives 18 in combination with theforward drive of such strands from the extruder will project thethus-formed pellets radially forwardly of the die face in compositetrajectories determined by such factors as the extrusion rate and thespeed at which the knives are rotated. In order to capture and collectsuch formed pellets, the coolant cage 10 constructed in accordance withthe present invention is provided.

Such coolant cage may be of generally cylindrical or conicalconfiguration that is adapted for nonrotational fixed support adjacentthe front face 16 of the die 12 as by engagement with ledge 50 of acircumferential plate 51 and a cooperating retaining ring 52. The cageincludes a peripheral side 53 forming an internal side surface 54 and afront face member 55 forming an internal forward surface 56. The sidesand front face 53, 55 may be of one-piece, integral construction orinterconnected by means of a bridging member 58 depicted, it being clearthat the internal surfaces 54, 56 compositely form an enclosing chamber60 in which the pellets so formed are entrapped. In addition, theforward surface 56 may be provided with an access and/or viewing port orports 62 having a clear window 64 formed of plastic material, such as"Lexan" and the like, retained in position by retainer 66 in such amanner to insure a smooth transition with remaining interior portions ofthe surface 56. Similarly, the walls 53 of the cage 10 forming theinternal side surfaces 54 may be also provided with access and/orviewing ports in order that the granulation process conducted thereinmay be readily observed and adjustments to operating parametersaccordingly made in light thereof.

It may thus be seen that pellets as they are formed will assume varioustrajectories as above indicated and make initial contact either with theinternal side surfaces 54 or the internal forward surface 56. Also,inasmuch as such pellets have at least portions thereof which are hot,and accordingly, should they contact either uncooled cage surfaces oreach other while in such uncooled and potentially sticky state, they mayform clusters which are undesirable in later processing of the pellets,as, for example, in their use as feed material in final article formingextrusion processes where they are weighed, conveyed and screw injected.It is accordingly imperative that such individual pellets be immediatelycooled so that they will not either form clusters or stick to theinternal surfaces of the coolant cage.

The present invention accomplishes such objectives by the simultaneousprovision in both internal surfaces 54 and 56 of separate coolant flowssubstantially over these surfaces. In this regard, a first coolant flow68 is directed about the internal side surfaces 54 in a peripheral orbitby means of a first distributing assembly 70 comprising a housing 72attached to the outside of the hood, including a conduit 73 to supplycooling fluid under pressure to a channel 74 through the wall 53 andinto contact with a diverter element 76 which serves to tangentiallyforce coolant in a thin film in an arcuate path about the innerperiphery of the hood side wall surfaces 56. The diverter 76 is of atransverse extent so that the coolant flow 68 is placed substantiallyacross the entire extent of the side wall surface 54. Such housing 70may be disposed preferably on top of and supported by an exit tube 78for conveying the coolant entrained particles outwardly of the hood froman exit opening 80 of significant radial extent and similarly extendingsubstantially entirely transversely across said inner wall surfaces 54.At such location, such exit tube 78 may be vented as at 82 to preventair pressure resistance.

The first coolant entrance means 70 is also preferably disposedimmediately proximal the exit opening 80 and in such a manner that thefirst coolant flow across the internal surfaces 54 is adapted to makesubstantially a single-pass peripheral orbit thereabout prior to itsexit. In this way, then, pellets contacting such side surfaces 54 areimmediately entrained in coolant flow 68 to cool them and thereafterconveyed outwardly of the chamber 60 in less than a single orbit of suchcoolant flow about the internal surfaces 54. Those pellets thusinitially contacting surfaces 54 proximal the coolant entrance 70 makesubstantially a complete orbit while those initially contactingdownstream portions thereof will make substantially less than suchsingle orbit. Also, pellets initially diverted into the exit opening 80will be entrained therein and cooled by the flow of coolant sweptthereinto. Although more than one such first coolant entrance means 70may be utilized, that is, spaced about the periphery of cage side walls53, one such means positioned as above indicated has been foundsatisfactory.

Simultaneously, the forward surface 56 is provided with a second coolantflow 83 which is directed radially outwardly from a central pointproximal the knife carrier 22 toward the first circumferential movingcoolant flow 68 in such a manner so as to converge therewith at thetransition portions of the surfaces 54, 56, as at 58, and in this mannernot only provide a nonstick, cooled forward surface 56 but furtherdirect pellets initially contacting said surface into the first radialcoolant flow 68 so as to assure their prompt exit from the chamber 60.Also dependent on the direction of the radial component of the secondcomponent, it will either merge with the first coolant, as when thesedirections are the same, somewhat smoothly but still believed to produceeddy-type currents and resultant nonlaminar flow creating coolant spray,mist, etc., to enhance cooling entrainment of the pellets, or will, whenthese directions are opposed, merge less smoothly, causing further spraybut believed to consume more energy and having greater potential forpellets to be projected out of the coolant flows into contact withoncoming pellets subsequently formed and in trajectories towards saidmerging coolant flows. The above operational theory is believed to beconsistent with operational experience of the present invention and isset forth for purposes of explanation only, rather than limitation.

The radial outward second coolant flow is provided by means of a secondcoolant assembly 84, including a housing 86 adapted for nonrotationalfixed support to outer portions of the cage 10, proximal the centralopening 88 provided therein for receipt of the hub 24 outwardlyprojecting therefrom and the rotating knife retaining means 22. Suchhousing 86 includes one or more conduits 90, there being three depictedin the drawings, for directing a coolant flow radially and tangentiallyonto the forward surface 56 of the chamber 60 by contact with a spinneror slinger member 91 having an inwardly directed radial flange 92, theforward terminous 94 of which is spaced slightly from the forwardsurface 56 and in this manner forms a secondary channel 96 for receiptof coolant fluid radially outwardly across the foward surface 56. Inorder to evenly space such second coolant flow over the forward surface56, it has been found desirable to incorporate a plurality of spacedbaffles 98 which serve to receive such second coolant flow from conduit90 and project such radially outwardly in an efficient manner. Tofurthermore conserve energy in accomplishing such outward divergentflow, the conduit 90 is provided with a tangentially disposed secondaryconduit 99 and as best shown in FIG. 5. The slinger 91 in turn is fixedto outer portions of the knife retainer 22 by known means and mayinclude a forward extension 100 adapted to sealingly engage a downwardlyextending flange 102 provided in the housing 86 so as to block exit ofthe coolant therebetween. The coolant anticipated for use hereabove iscooled water, although various other coolants as may be appropriate maybe utilized.

Thus, upon operation of the device above described, the pellets as theyare formed and as they enter the chamber 60 are immediately entrained ina coolant flow regardless on which surface they initially contact, andsuch coolant flows are regulated in such a manner so that pellets areimmediately entrained, cooled and exited from such chamber in anextremely short dweel time and thus are not available for secondarycontact with subsequently formed pellets. This action reduces the chanceof cluster formation in a highly efficient manner and utilizingefficient, easy-to-reproduce equipment to accomplish the severalaforesaid objectives of the present invention.

While there is shown and described herein certain specific structureembodying the invention, it will be manifest to those skilled in the artthat various modifications and rearrangements of the parts may be madewithout departing from the spirit and scope of the underlying inventionconcept and that the same is not limited to the particular forms hereinshown and described except insofar as indicated by the scope of theappended claims. For example, the terms "raidial" or "radially" as usedherein mean generally in a radial direction including moving from acentral area outwardly towards a peripheral area rather than beinglimited to travel from a center point along a radius thereof.

What is claimed is:
 1. In a method of forming discrete thermoplasticresin pellets by extruding, the improvement comprising directing saiddiscrete thermoplastic resin pellets, at least portions of which are ina hot, sticky condition, radially outwardly and forwardly into initialcontact with internal side or forward surfaces of an enclosing chamber,directing a first coolant flow over and in contact with a major portionof said side surface while simultaneously directing a second coolantflow radially outwardly over and in contact with a major portion of saidforward surface to entrain and pellets upon initial contact with saidchamber in one of said coolant flows, cooling said pellets andthereafter removing substantially all of said pellets from said chamberin less than a single pass peripheral orbit about said side surfaces. 2.The method of claim 1 including slinging coolant from central forwardportions of said chamber radially outwardly over said forward surface bymeans of a rotating flange having a plurality of spaced baffles.
 3. Themethod of claim 2 including directing coolant flow tangentially againstsaid baffles in the rotational direction of said flange.
 4. The methodof claim 1 including introducing said first coolant flow along a linesubstantially entirely across the transvert extent of said side surfaceand removing said entrained cooled pellets at a point essentiallyimmediately upstream adjacent thereto.
 5. The method of claim 1including directing said second coolant flow radially outwardly intocomingling contact with forward portions of said first coolant flow. 6.The method of claim 5, the peripheral area where said coolant flows joincreating a zone of nonlaminar flow.
 7. The method of claim 1 includingdirecting said second coolant flow against said forward surface with aradial component having the same direction as that of said first coolantflow.